I found this. I don't know what wireless card/driver you have, but your setup may show similar information:
Used to provide details on the channel capabilities enabled by the adapter.
% cat /sys/bus/pci/drivers/ipw3945/*/channels
Displaying 13 channels in 2.4Ghz band (802.11bg):
1: 17dBm: BSS, IBSS, active/passive.
2: 17dBm: BSS, IBSS, active/passive.